1. Field of the Invention
The present invention relates to lift trucks and more particularly to a lift truck having a horizontally rotatable load-handling apparatus.
2. Description of the Prior Art
There is no load-lifting apparatus known to be available that is adapted for use with conventional lift trucks and capable of rotating large, heavy containerized loads or other similarly large objects through a substantial arc of at least 180.degree. about a vertical axis.
The need for such an apparatus has arisen because of the recent development of a system of shipping automobiles inside large containers to prevent damages to the automobiles while in transit from theft, vandalism and natural hazards. Each such container has one open end and contains three automobiles. Several such containers are loaded close together end-to-end on a railroad flatcar with their open ends being adjacent to an end of an adjoining container so as to be inaccessible. When the flatcars reach their destination, the containers are lifted therefrom and placed on the ground ready for unloading. If stored for any length of time on the ground, such containers again may be placed close together with their open ends unexposed and inaccessible.
In the loading, unloading and general handling of such containers, large heavy-duty lift trucks are used. The work of such trucks would be greatly simplified if their load-lifting apparatus could rotate the containers through at least 180.degree. because of the frequent need to reverse the containers end-for-end for proper positioning of the containers. With such a rotatable apparatus the open ends of the containers could be easily oriented with respect to machines used for inserting automobiles into and extracting automobiles from the containers, for loading the containers on flatcars and for placing the containers in storage positions without the need for excessive maneuvering of the lift truck itself.
There are presently load carriages available for use with lift trucks capable of limited pivoting movement of a load through an arc of about 10.degree. about a vertical axis. However, such carriages would obviously not be suitable for the foregoing-described purposes.
Although some prior patents suggest load-handling apparatus for vehicles capable of rotating loads about a vertical axis, such apparatus either requires a special-purpose vehicle or provides for rotation through only a limited arc of considerably less than 180.degree. or would obviously not be adapted to handle large, heavy container-sized loads. Still other prior patents suggest such rotatable load-handling apparatus for lift trucks, but without clearly disclosing the nature of the rotating mechanism intended to be used. The closest known prior patents disclosing such apparatus are U.S. Pat. Nos. 2,620,930; 2,699,879; 3,003,206; and 3,638,810.
In the prior art, a common means of turning a shaft or other mechanism is through the use of a hydraulic, air or electric motor coupled with a gear, belt or chain drive reducer. This means has two disadvantages for the intended application. First, such a rotating unit powerful enough to turn and stop the heavy loads that are involved would be too expensive. Second, precise positioning of a load with such means is difficult to achieve.
Accordingly, in the design of a suitable rotatable apparatus to meet the previously described needs, it is desirable to use fluid-powered cylinders to achieve the desired rotational movement. Fluid power is readily available from lift trucks, and fluid cylinders can develop high turning forces for their size and weight as compared to other motors. Furthermore, precise positioning control is possible with fluid cylinders, and cylinder-operated mechanisms are usually easy to service. However, in the known state of the art, fluid cylinder operated mechanisms are not capable of pivoting a shaft in opposite directions through more than about 100.degree., which is insufficient for the application proposed.
Thus there is a need for a fluid cylinder operated mechanism capable of rotating a load-handling apparatus of a lift truck in opposite directions through at least 180.degree.. Moreover there is a need for a load-handling apparatus with such a rotation mechanism that is adapted for use with conventional lift trucks and that is capable of handling container-size heavy loads.